This invention relates to an oscillation mechanism for producing high-frequency oscillation upon a stage being positioned very precisely. In another aspect, the invention concerns an exposure apparatus having such an oscillation mechanism and/or a device manufacturing method using the same.
In exposure apparatuses, for the manufacture of a very fine pattern such as a circuit pattern of a semiconductor device, further decreases in linewidth of a transferred pattern and further increases of throughput are desired. For a narrowed linewidth of a transferred pattern, the wavelength of exposure light to be used for an exposure process should be shortened more, and the wavelength shortening has been made by using g-line light, i-line light, KrF laser light and so on. As regards synchrotron radiation light emitted from a synchrotron ring, because the wavelength thereof is short, it has an advantage in transferring a very fine pattern and attracts much attention as exposure light in an exposure apparatus.
The synchrotron radiation light emitted from a synchrotron ring comprises a sheet-like beam having a small thickness in a vertical direction. Proposals have been made in relation to it, to oscillatingly move an X-ray mirror for reflecting and directing the sheet-like synchrotron radiation beam to an exposure region, so as to scanningly deflect the beam upon the exposure region thereby to substantively expand the beam irradiation region with respect to the vertical direction.
An example of such an X-ray exposure apparatus is disclosed in Japanese Laid-Open Patent Application, Laid-Open No. 321007/1995. FIG. 4 shows such an exposure apparatus, wherein denoted at 101 is synchrotron radiation light (hereinafter, xe2x80x9cSR beamxe2x80x9d) emitted from a synchrotron ring, not shown. Denoted at 102 is an X-ray mirror for reflecting the SR beam 101, and denoted at 103 is an oscillation mechanism for oscillating the X-ray mirror 102. Denoted at 104 is a reference stage for holding the X-ray mirror 102 and the oscillation mechanism 103, and denoted at 105 is an X-ray position detector for detecting the position of the SR beam 101, wherein the detector 105 is mounted on the reference stage 104. Denoted at 106 is a mirror chamber for accommodating therein the X-ray mirror 102, the oscillation mechanism 103, the reference stage 104 and the like, and the inside space of the mirror chamber is kept at an ultra-high vacuum. Denoted at 107 is a driving mechanism for adjusting the position and posture of the reference stage 104, and denoted at 108 is a computing unit for processing an output signal of the X-ray position detector 105 to calculate the position of the SR beam 101. Denoted at 109 is a drive control mechanism for actuating the driving mechanism 107 in response to a signal from the computing unit 108. Denoted at 110 is a chamber holding unit for securing the mirror chamber 106 on a floor.
In the X-ray exposure apparatus with the structure described above, the position of the SR beam 101 is detected by the X-ray position detector 105. Then, by using the computing unit 108, the drive control mechanism 109 and the driving mechanism 107, the X-ray mirror 102 is positioned with respect to the SR beam 101. While keeping that position, the X-ray mirror 102 is oscillated by the oscillation mechanism 103 with a predetermined amplitude. With this oscillation of the X-ray mirror 102, the SR beam of sheet-like shape is scanningly deflected along the exposure region, whereby the beam irradiation region is substantively expanded.
However, the oscillation mechanism such as described above and incorporated into an exposure apparatus involves inconveniences as follows.
If, for example, an oscillation element such as an X-ray mirror is bulky or if the frequency or amplitude of oscillation is large, a large oscillation force is required to produce oscillation of the oscillation element (X-ray mirror) at the predetermined frequency or amplitude. This necessarily cause a large reaction force which is transmitted from the oscillation mechanism to the reference stage for holding the oscillation mechanism. This means a large external disturbance to the reference stage, which causes degradation of the controllability of the reference stage position and thus, degradation of the positioning precision of the SR beam with respect to its positioning reference, for example.
Particularly, in the exposure apparatus as shown in FIG. 4 and in a case where the SR beam 101 is substantively expanded by the X-ray mirror 102 to irradiate the whole mask surface at once (whole surface exposure), if there is an error in shape of the mirror reflection surface or non-uniformness of reflection factor thereof, it directly causes non-uniformness of the intensity of the SR beam projected on the mask surface. In order to average such non-uniformness, it would be necessary to produce high-speed micro-vibration of the X-ray mirror to cause averaging of the SR beam irradiation intensity on the mask surface, as illustrated in FIG. 3. However, if high-speed micro-vibration of the X-ray mirror 102 is produced, it causes vibration of the reference stage 104, holding the X-ray mirror 102 and the oscillation mechanism 103, due to external disturbance. This results in degradation of the positioning precision of the X-ray mirror 102 with respect to the SR beam 101. Uniform irradiation intensity of the SR beam upon the mask surface is therefore unattainable.
It is accordingly an object of the present invention to provide an oscillation mechanism by which the positioning precision with respect to a certain positioning reference is not degraded even if an oscillation element such as an X-ray mirror is oscillated or vibrated with a predetermined frequency and/or a predetermined amplitude.
It is another object of the present invention to provide an exposure apparatus with such an oscillation mechanism incorporated thereon, by which an X-ray mirror is oscillated or vibrated with a result of uniform SR beam irradiation intensity on a mask surface.
It is a further object of the present invention to provide a device manufacturing method using such an exposure apparatus.
In accordance with an aspect of the present invention, there is provided an oscillation mechanism, comprising: a measuring device for measuring a position of an object; a movable stage being arranged so as to be positioned with respect to the object; a driving mechanism for moving said stage; a control unit for controlling said driving mechanism on the basis of an output of said measuring device; an oscillation element mounted on said stage and being arranged to be oscillated at a predetermined stroke; an intermediate structure having a predetermined mass and being disposed between said stage and said oscillation element; a spring element for coupling said intermediate structure, said stage and said oscillation element with each other; and an oscillating unit for oscillating said oscillation element at a predetermined frequency.
The oscillating unit may be operable to change the oscillating frequency continuously.
The oscillating frequency of said oscillating unit may be changed continuously to determine an oscillating frequency with which vibration to be applied to said stage is minimized.
The oscillating unit may include a piezoelectric device.
In accordance with another aspect of the present invention, there is provided an exposure apparatus, comprising: a light source; a measuring device for measuring a beam from said light source; a movable stage being arranged so as to be positioned with respect to the beam; a driving mechanism for moving said stage; a control unit for controlling said driving mechanism on the basis of an output of said measuring device; an oscillation element mounted on said stage and being arranged to be oscillated at a predetermined stroke, said oscillation element holding an optical element; an intermediate structure having a predetermined mass and being disposed between said stage and said oscillation element; a spring element for coupling said intermediate structure, said stage and said oscillation element with each other; and an oscillating unit for oscillating said oscillation element at a predetermined frequency.
The light source may comprise a synchrotron radiation light source.
The optical element may comprise a mirror.
The oscillating unit may be operable to change the oscillating frequency continuously.
The oscillating frequency of said oscillating unit may be changed continuously to determine an oscillating frequency with which vibration to be applied to said stage is minimized.
The oscillating unit may include a piezoelectric device.
In accordance with a further aspect of the present invention, there is provided a device manufacturing method, comprising the steps of: applying a photosensitive material to a wafer; exposing the wafer by use of an exposure apparatus as recited above; and developing the exposed wafer.
In an oscillation mechanism according to the present invention, an oscillation element to be oscillated with a predetermined stroke and oscillating means for oscillating the oscillation element at a predetermined frequency are mounted on a stage which is to be positioned. Also, an intermediate structure having a predetermined mass is disposed between the stage and the oscillation element. The intermediate structure, the stage and the oscillation element are coupled by a spring element or elements. The oscillating means is disposed between the intermediate structure and the stage. On the basis of the frequency and amplitude for oscillating the oscillation element, spring constants of two springs and the mass of the intermediate structure are selected appropriately, by which the reactive force to be transmitted to the stage, supporting the oscillation element, can be reduced to zero. This prevents degradation of the positioning precision of the oscillation mechanism, such that high precision oscillation about the position taken by the positioning is attained.
The oscillating frequency of the oscillating means may be made variable continuously, and an oscillating frequency with which vibration to be applied to the stage is made smallest may be selected. The oscillation element may be oscillated with such frequency. Thus, even if there is an error in the mass of any component or in the spring constant of a leaf spring, for example, with respect to a design value, due to a machining error, for example, external disturbance to be applied to the stage can be minimized or be fully avoided.
The oscillating means for the oscillation element may comprise a piezoelectric device. On that occasion, the stage can be made compact and light in weight, and the oscillation element can be oscillated at a higher frequency.
In an exposure apparatus according to the present invention, advantageous effects provided by the positioning mechanism such as described above are also attainable and, additionally, an X-ray mirror can be oscillated at a high speed while being positioned precisely with respect to the SR beam. Thus, uniform SR beam irradiation intensity is attainable upon a mask surface.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.